The present disclosure relates to semiconductor structures, and particularly to a metal-oxide-semiconductor field effect transistor (MOSFET) having a high performance replacement gate electrode configured to provide reduced parasitic capacitance and/or low resistance, and methods of manufacturing the same.
A replacement gate metal-oxide-semiconductor field effect transistor (MOSFET) can accommodate a high dielectric constant (high-k) gate dielectric material that is prone to degradation at high temperature due to decomposition or other structural degradation mechanisms. A replacement gate MOSFET is formed by forming activated source and drain regions and optionally metal semiconductor alloys before deposition of a gate dielectric and a gate electrode. A replacement gate MOSFET employs a recessed region, which is typically referred to as a “gate cavity,” that is subsequently filled with a gate dielectric and a gate electrode. The recessed region is typically formed by removing a disposable gate structure. Because the gate dielectric and the gate electrode “replaces” the disposable gate structure by filling the gate cavity, the gate dielectric material, which is typically a high-k gate dielectric material, follows the contour of the recessed region.
A challenge in employing the replacement gate scheme to manufacture high performance devices is to fill gate cavities with a conductive material having a high conductivity. The overall conductivity of replacement gate conductor structures is limited due to the relatively high conductivity of materials employed as work function material layers. While the optimal work function material layers can provide appropriate work function levels for p-type field effect transistors and n-type field effect transistors, respectively, such work function material layers do not provide as high conductivity as a conductive fill material that fills the remaining portion of a gate cavity. Further, the presence of the work function material layers on sidewalls of gate cavities reduces the width of the gate cavities so that the volume that the conductive fill material can occupy is reduced. In addition, reduction of width with scaling in conjunction with the presence of work function material layers on sidewalls of gate cavities can cause formation of voids during the filling of the gate cavities with the conductive fill material. The combination of the above factors contributes to a significant increase in the resistivity of gate conductors in replacement gate structures as device scaling continues, and limits performance of advanced replacement gate field effect transistors.